1. Field of the Invention
The present invention relates to a transmitter and receiver of digital video signal capable of transmitting at a low bit rate.
2. Description of the Related Art
Digital video data of a dynamic image contains a very large amount of information and a transmission bit rate becomes very high if it is transmitted as it is. Due to that, conventionally data is compressed taking an advantage that generally an image is information of time and space when it is transmitted using a low rate transmission medium whose transmission bit rate is limited in a same manner as digital video data is recorded or reproduced using a magnetic tape or magneto-optic disk.
The compression and transmission of digital video signal have been conventionally carried out for example by taking a difference between frames of digital video data and by data compressing the difference using DCT. (discrete cosign transform). Further, considering that there are less motions in video, data is transmitted culling out its amount in a TV conference by transmitting data of only single side field, not transmitting full frames.
Although the image may become fine by victimizing time data and by assuring space data by reducing a number of fields to be transmitted, not transmitting the single side fields, the motion may become awkward.
However, because a quality of the dynamic image is lost if the motion is awkward, a method of transmitting a full frame by compressing image data per one frame as much as possible to be able to reproduce a full motion as a dynamic image is being considered.
As described above, the conventional method for transmitting digital video signal is devised so that the transmission rate is lowered by compressing video data in the time direction or spatial direction.
However, if the transmission bit rate is to be lowered just by compressing data, i.e. by compressing in the time direction for example, a motion of the dynamic image becomes awkward and an unnatural video is brought about. Further, if data is compressed in the spatial direction, the spatial resolution is degraded that much, degrading the reproduced video.
That is, because the conventional method lowers the bit rate just by compressing data, it victimizes either or both data in the time direction and spatial direction, disallowing to obtain a satisfactory reproduced video.
Accordingly, it is an object of the present invention to provide a transmitter and receiver for digital video signal devised to be able to obtain a beautiful reproduced video as much as possible and in the same time, to render the motion smooth.